1. Field of Invention
The present invention relates in general to the fields of removability, reworkability and recyclability. More particularly, the present invention relates to a method and apparatus employing microcapsules adapted to rupture in a magnetic field to enable a first substrate (e.g., a coldplate) to be easily removed from a second substrate (e.g., an electronics module) for enhanced reworkability or recyclability.
2. Background Art
In general, it is desirable for a thermal interface material (TIM) gap filler between a first substrate (e.g., a coldplate) and a second substrate (e.g., a cap of an electronics module) to exhibit adequate adhesion (i.e., the thermal performance of the interface is reduced if an air gap is introduced from voids or delamination), yet possess a low enough bond strength to allow for rework. In the case of a “TIM2” gap filler (e.g., between a bottom surface of a coldplate and a top surface of a cap of an electronics module), for instance, it is desirable for the TIM gap filler to exhibit adequate adhesion to both the bottom surface of the coldplate and the top surface of the cap of the electronics module, yet possess a low enough bond strength between itself and the coldplate to allow for rework. In this case, the coldplate must be completely removed from a defective electronics module to provide reworkability to the module during manufacture or in the field. Several approaches to address this problem have focused on a pad TIM2 and a cross-linked silicone gel. A serious drawback to the first approach (i.e., a pad TIM2) is that pads are not compressible enough, resulting in poor thermal performance at the interface. A serious drawback to the second approach (i.e., a cross-linked silicone gel) is that gels can “pump” out of the interface due to thermal cycling. Another approach to address this problem is to utilize a picture-in-picture-frame concept, wherein the “picture frame” is comprised of a pad and the “picture” is comprised of a cross-linked silicone gel. In the case of this hybrid approach, the pad prevents the gel from pumping; and because the bulk of the TIM gap filler is a gel, adequate compression to the desired bond line is provided. However, the hybrid approach disadvantageously requires the use of two distinct TIM gap filler materials, as well as a custom die-cut pad.
Although described in the context of removing a coldplate adhered to an electronics module by a TIM gap filler, the problem discussed above also exists in the more general context of removing one substrate from another. For example, a similar problem exists in the context of removing a first substrate from a second substrate for purposes such as recycling, reworkability, and the like. In one illustrative example, labels are frequently attached to products, such as computers and other electronic devices, for purposes of information, safety and security. Typically, an adhesive layer permanently affixes the label to the product to prevent the label from falling off or being removed from the product. For example, the use of pressure sensitive adhesive (PSA) labels for such purposes is well known in the art. Typically, the pressure sensitive adhesives used on these labels are extremely tenacious and tend to exhibit exceptional adhesion well beyond the lifetime of the product. Removable labels, i.e., labels provided with a removable adhesive layer possessing temporary as opposed to permanent bonding characteristics, are known in the art but are typically not used because of the increased likelihood that such labels will fall off the product and because such labels undesirably enable inappropriate removal by the user. For example, it is generally undesirable for a user to remove a safety label from a cover of a computer enclosure.
Hence, labels that are permanently affixed to the product are typically preferred from a product use perspective. From the recycling perspective, however, labels that are permanently affixed to products are problematic. Typically, the label must be removed from the product before it is possible to recycle the label-bearing part of the product. Generally, the removal of permanently affixed labels is a difficult and time consuming task and often results in unsatisfactory results, i.e., remnants of labels and/or adhesive residue may remain on the product. Contamination by the label remnants and/or adhesive residue makes it practically impossible to recycle products bearing permanently affixed labels. The wasteful and undesirable practice of burying the label-bearing parts of such products in landfills is often the only available disposal technique. Depending on the composition of the label-bearing parts, incineration may be an available alternative disposal technique, but generally is also a wasteful and undesirable practice.